Zooplankton are a diverse group of tiny animals that float freely in the water column and feed on phytoplankton (plant plankton) and other zooplankton. This group includes jellyfish and comb-jellies, small crustaceans like copepods and krill, the larval forms of crabs and oysters, the larval or juvenile forms of some fish, and many other organisms. This Vital Sign tells us about the abundance and distribution of zooplankton populations in Puget Sound. Zooplankton play a critical role in the marine food web as important prey for juvenile salmon and small forage fish.


Key Vital Sign Messages

  • The Puget Sound Zooplankton Monitoring Program was initiated in 2014 to address the effects of prey limitations on juvenile salmon survival in their critical growth phase, and is an ongoing monitoring program involving numerous contributors, including state, federal, tribal, and local agencies.  
  • The zooplankton monitoring data fill long-standing data gaps for fishery managers and ecosystem modelers and have shown correlations to salmon survival. Zooplankton communities are seasonally distinct throughout the several basins in the southern Salish Sea, and changes in their communities can be tied to large-scale climate fluctuations.  
  • The mechanisms affecting zooplankton populations in the Salish Sea and its unique basins vary from those on the outer coast, making regional studies of Salish Sea zooplankton critical for understanding local causes and effects of changing zooplankton communities.
    • More than 200 species of zooplankton have been identified in the top 200 m of the water column.
    • Copepods are the most abundant taxonomic group in the southern Salish Sea, consisting of >70 species and often >50% of the biomass.
    • In addition to copepods, other abundant taxa include barnacles, larvaceans, gastropods, bryozoans, bivalves, polychaetes, cladocerans, and amphipods.  
  • During the Pacific marine heatwave of 2015-2016, zooplankton biomass was anomalously high throughout most regions, which persisted in Puget Sound through 2017, with the most dramatic increases seen in central Puget Sound stations. 

Background Documents

Indicator Targets 

Targets have not yet been defined for these indicators. When evaluating trends in the indicators, it is important to note that high biomass of any group would indicate high prey availability for their predators. However, because there is a complex food web in the Salish Sea where sustained predation will decrease biomass, low biomass does not necessarily indicate that the system is in an unhealthier state than when biomass is high.

Other Resources



Winans, A. K., B. Herrmann, and J. E. Keister. 2023. Spatio-temporal variation in zooplankton community composition in the southern Salish Sea: changes during the 2015-2016 Pacific marine heatwave. Progress in Oceanography. Accepted. 

Khangaonkar, T., A. Nugraha, S. K. Yun, L. Premathilake, J. E. Keister, and J. Bos. 2021. Propagation of the 2014–2016 northeast Pacific marine heatwave through the Salish Sea. Frontiers in Marine Science 8. https://doi.org/10.3389/fmars.2021.787604

Khangaonkar, T., A. Nugraha, L. Premathilake, J. E. Keister, and A. Borde. 2021. Projections of algae, eelgrass, and zooplankton ecological interactions in the inner Salish Sea – for future climate, and altered oceanic states. Ecol. Modell. 441: 109420. doi:10.1016/j.ecolmodel.2020.109420 


Contributing Partners

Zooplankton Vital Sign indicators development


Puget Sound Zooplankton Monitoring Program development & management


Puget Sound Zooplankton Monitoring Program/Salish Sea Marine Survival Project funding

  • The Salish Sea Marine Survival Project (Long Live the Kings and the Pacific Salmon Foundation for program development and 2014 and 2015 sampling and analysis)
  • King County (for Central Basin sampling, analysis, and CTD data)
  • The NOAA Saltonstall-Kennedy Program and Tulalip Tribes (for 2016 sampling and analysis)
  • The Environmental Protection Agency
  • WA Dept. of Natural Resources (for 2017-2021 sampling and analysis

Zooplankton field samplers & coordinators

  • King County
  • Kwiáht Center for the Historical Ecology of the Salish Sea
  • Lummi Nation
  • Nisqually Indian Tribe
  • NOAA
  • Port Gamble S'Klallam Tribe
  • WA Dept. of Fish and Wildlife
  • Tulalip Tribe
  • Hood Canal Salmon Enhancement Group
  • WA Dept. of Ecology
  • Stillaguamish Tribe of Indians
Related Strategies
Amanda Winans, UW Oceanography. Key messages were reviewed by the PSEMP Forage Fish Work Group.
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